Covered California officials said Thursday they're scrambling to reach nearly 10,000 people across the state who will lose their health insurance subsidies unless they give an OK to have their income verified.

The issue revolves around 24,000 people who didn't provide the consent that enables them to receive the income-based subsidies that can reduce premiums of a 55-year-old single man in Ventura with an income of $35,000 by more than $400 a month, according to Covered California estimates.

Because Covered California — the health insurance marketplace created through the Affordable Care Act — didn't realize consent was not given, the people were sent notices telling them they were in line to receive the subsidies that come in the form of tax credits. That message was wrong, said James Scullary, a Covered California spokesman.

"We cannot provide the tax credits without consent to verify the consumer's income," he said Thursday, noting that the consent is required by Dec. 31 under federal law.

Of the 24,000, more than 14,000 people have been reached through phone calls, emails and letters, Scullary said. They've been told they can provide consent before the New Year's Eve deadline through a phone call, by going online or by enlisting the help of an enrollment agent.

Scullary said Covered California is scrambling to make contact with about 9,600 people.

"We have reached out multiple times through phone calls, emails and letters — and are planning to send another email this week," he said.

If people don't take action, they may suffer sticker shock when they open their January insurance bill. Instead of paying the full premium, they should contact Covered California and provide the needed income consent, Scullary said. Then their insurer will be instructed to send a new bill that includes the subsidy.

According to the most recent data, about 34,530 Ventura County residents are covered this year under plans bought through Covered California. Officials reported earlier this month that statewide enrollment for 2017 was ahead of last year's pace, with more than 150,000 new enrollees. They said more than 1.2 million Californians renewed their coverage.

Enrollment for 2017 continues through Jan. 31. President-elect Donald Trump has pledged to repeal and replace the Affordable Care Act that enabled the creation of Covered California and other health insurance exchanges across the nation.

Jim Nicoll, a certified Covered California insurance agent in Ventura, said he hasn't encountered clients in jeopardy of losing their subsidies because of the consent issue. He predicted any dramatic changes to Covered California will take time but also acknowledged the uncertainty.